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https://issues.apache.org/jira/browse/FLINK-1045?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14094759#comment-14094759
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Fabian Hueske commented on FLINK-1045:
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Exactly. I propose to remove the annotation and the default implementation and
check combinability by checking for the interface implementation. Since this is
a API breaking change, I would do it for 0.6 (if we do it).
Users that want to enable the combiner for a RichGroupReduceFunction would need
to provide an implementation instead of attaching the annotation (and implement
the combiner if they don't want to use the default implementation). With the
current implementation, the combinable annotation also needs to be attached for
UDFs that implement only the interface and not the rich function.
I find it a bit awkward that users needs to implement an interface and activate
the combinability with the annotation where the implementation would be
sufficient.
> Remove Combinable Annotation
> ----------------------------
>
> Key: FLINK-1045
> URL: https://issues.apache.org/jira/browse/FLINK-1045
> Project: Flink
> Issue Type: Improvement
> Components: Java API, Scala API
> Reporter: Fabian Hueske
> Priority: Blocker
> Labels: api-change
>
> Since the {{combine()}} method was extracted into an interface, we can check
> if a function is combinable by checking if the interface is implemented.
> Hence, the {{Combinable}} annotation could be removed, IMHO.
> However, this would change the API because {{RichGroupReduceFunction}} could
> no longer have a default implementation of {{combine()}} that can be enabled
> by attaching the annotation.
> Right now, the {{Combinable}} annotation is just not necessary as the
> implementation of the interface tells the system everything it needs to know.
> Removing the {{Combinable}} annotation would also make the handling of
> different combinable functions easier. For example a function that implements
> the interfaces {{GroupReduceFunction}} and {{FlatCombineFunction}} does not
> need to attach the annotation.
> Since this is not a big, but API changing change, I would like to get it into
> 0.6 (if we decide to do it).
> What do you guys think?
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